Chemical agent sensor having a stationary linear fringe interferometer

ABSTRACT

A sensor having an input to an interferometer. The input may receive emissions from a detected fluid. The output of the interferometer may be focused on an array of light detectors. Electrical signals from the detectors may go to a processor. The output of the processor may include a spectrum of the detected fluid. Also, the identity of the fluid may be determined.

BACKGROUND

This present application is a continuation-in-part of U.S. patentapplication Ser. No. 10/324,314, filed Dec. 19, 2002, now U.S. Pat. No.6,946,644, by R. A. Wood, and entitled “MULTI-BAND SENSOR”.

The invention may pertain to sensors and in particular to sensors fordetecting the presence of fluids and other substances. Moreparticularly, the invention may pertain to sensors that have detectorsensitivities of several bandwidths. “Fluid” is a generic term thatincludes liquids and gases as species. For instance, air, water, oil,gas and agents may be fluids.

The related art might detect at several wavelengths; however, theresults of detection may not be sufficiently accurate because of sensorstructure or other impediments resulting in different fields of view fordetection at different wavelengths.

SUMMARY

The invention may be a multi-band sensor for detecting various fluidshaving emissions with various wavelengths and intensities.

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1 a, 1 b and 1 c show upward and downward fields of view for asensor;

FIG. 2 shows the sensor relative to a gas cloud and the sky.

FIG. 3 illustrates a thermoelectric detector;

FIGS. 4 a and 4 b reveal the sensor in conjunction with a vacuumpackage;

FIG. 5 is a layout of the detectors and filters of the sensor;

FIG. 6 is a graph showing transmission peaks of two thin-filminterference filters;

FIG. 7 is a layout of detectors and their connections into groups;

FIG. 8 is a side view of several detectors and their correspondingfilters;

FIG. 9 is a schematic of some electronics for the sensor;

FIGS. 10 a, 10 b and 10 c show absorptivity coefficients of an agent andtwo interferents;

FIG. 11 shows the effect of variation of an angle of incidence on anarrow-band filter;

FIG. 12 reveals a light integrating sphere;

FIG. 13 is a table of dimensions for a sensor;

FIG. 14 is a diagram of a multi-band gas sensor;

FIG. 15 is a graph of an interference pattern of light that impinges alinear detector array; and

FIG. 16 is a graph of a spectrum of a detected gas or gases.

DESCRIPTION

The device may be a multi-band sensor for chemical agents or othersubstances in the atmosphere, suitable for flight on micro air vehicles(MAVs), dispersal from aircraft, or other low-cost light-weightapplications. The sensor may sense the infrared (IR) emission at severalselected narrow wavebands in the 3–5 or 8–12 μm IR spectral region atwhich gases (exhaust fumes, chemical agents, etc.) show characteristic“fingerprint” infrared absorption and emission lines. The sensor may useuncooled silicon micromachined IR detectors in a silicon vacuum package.The sensors and detectors may be any kind of technology. IR detectorsare an illustrative example here. The estimated size, weight and powerof a complete sensor (less downlink transmitter and battery) are 1 cc, 4grams, 0.5 mW.

The sensor may be a multi-band IR sensor with a field of view directedupwards (dispersed or ground-based sensor) or downwards (MAV sensor)depending on the mission purpose. For exhaust gas detection, at leastone IR band may be centered on the absorption line of a component ofexhaust gas (CO₂, H₂O, CO, NO_(x), depending on the engine and fueltype), and at least one IR band may be centered at a wavelength wherethese gases are transparent. The presence of exhaust gases may beindicated by an imbalance in the measured radiance at the two or morewavelengths. The imbalance may be produced by the different emissivityand temperature of exhaust gas components. For a downward looking MAVsensor, this imbalance may show a daily reversal of polarity, withcrossover (minimum sensitivity) in the morning and evening.

The magnitude of the imbalance is difficult to predict analytically fora MAV downward looking sensor, since it may be strongly dependent ontime of day, wind dispersal, etc., but may be easily measurable, sinceengines produce large volumes of exhaust gases (a 1000 cu inch engineproduces about 100 liters per second at 1000 rpm idle).

An estimate of sensitivity may be more tractable for an upward lookingsensor. It may be shown with calculations that hazardous chemical agentscould be detected by an upward looking IR sensor. Such sensor mayoperate by sensing the radiance change caused by IR emission from theagent dispersed at altitudes where the air temperature is different fromthe apparent sky temperature. Using GB (Sarin), a particular chemicalnerve agent, as an example, and assuming a local air temperature 1degree C. different from the apparent sky temperature, C=10 mg/m3 of GBdispersed in a cloud L=10 m thick would produce an apparent temperaturechange of about 100 mK in a 20 cm-1 IR band centered at 1020 cm-1. Theapparent sky temperature change induced in a nearby IR band where GB istransparent (1250 cm-1, 8.0 um for example) is negligible in comparison.The IR signal from such a cloud of GB may therefore be detected (S/N≈5for CL≈1100 mg/m2) with a very low false alarm rate (about 2 e–6) withan IR sensor with a noise equivalent target temperature difference(NETD) of 20 mK in a 20 cm-1 radiation bandwidth 1020 cm-1. To cancelout variations in the sky temperature, the sensor would measure thefractional change in radiance with two IR sensors fitted withnarrow-band IR transmission filters (e.g., for GB, 20 cm-1 bands at 9.8and 8.0 um).

FIGS. 1 a and 1 b are illustrations of a downward-looking and anupward-looking sensor 10, respectively, with two IR detectors operatingat narrow-band wavelengths λ1 and λ2, which sense the infrared radianceof a gas cloud 11 (λ1) and with a ground 12 or sky 13 background (λ2).FIG. 1 c shows several upward-looking dispersed sensors 10 which mayprovide a protective surveillance of toxic agents for a specific area.FIG. 2 shows sensor 10 looking towards a warm gas cloud 11 beingcontrasted against a cold sky 13. Sensor 10 may have a multi-band IRarray 14, amplifiers 15 and processor 16. More than two IR wavebands canbe employed. An IR thermoelectric (TE) detector and an integrated vacuumpackage (IVP) may be applicable here. An illustrative example of suchdetector may be in U.S. Pat. No. 5,220,189, issued Jun. 15, 1993, withinventors Robert Higashi et al., and entitled “MicromechanicalThermoelectric Sensor Element”, which is hereby incorporated byreference. An illustrative example of such package may be in U.S. Pat.No. 5,895,233, issued Apr. 20, 1999, with inventors Robert Higashi etal. and entitled Integrated Silicon Vacuum Micropackage for InfraredDevices”, which is hereby incorporated by reference. The unit cell ordetector of this sensor consists of a thin (8000 A) silicon nitridemicrobridge, typically 50 to 75 um square, over a pit micromachined inthe underlying silicon substrate. Microelectomechanical systems (MEMS)techniques may be utilized in the making or fabrication of theinvention. Information about MEMS may be provided in U.S. Pat. No.6,277,666, issued Aug. 21, 2001, with inventors Kenneth Hays et al. andentitled “Precisely Defined Microelectromechanical Structures andAssociated Fabrication Methods”, which is hereby incorporated byreference. The sensors may operate by a thermal detection mechanism,i.e., incident IR radiation may heat the microbridge. Thin (1000 Å)thermoelectric metal films may form a thermocouple-pair and generate adirect voltage signal. Sensor 10 may be ‘self zeroing’ at anytemperature, and hence may not require a temperature stabilizer orhigh-bit A/D. FIG. 3 shows a cross-section of a TE detector 17. It mayhave electrical contacts 18 and 19 situated on a metal 20, a cold TEjunction 21 and a hot TE junction 22 of metals 20 and 23. Junction 22 issupported over an etched pit or well 24 by a silicon nitride bridge 25.All of this may be formed in and supported by a substrate 26. IRradiation 27 may impinge detector 17 which in response an electricalsignal noting the impingement appears at contacts 18 and 19.

TE detectors 17 or sensors should operate in a vacuum to achieve fullsensitivity (as any gas pressure more than 75 mTorr may dampen thethermal signals unacceptably). One may use a low-cost light-weightwafer-scale vacuum encapsulation using an IR-transparent silicon“topcap” 28 on a substrate 29 as shown in FIG. 4 a. FIG. 4 b illustratesthe basic fabrication of wafer-to-wafer bonding of topcat wafer 28 todevice wafer 29 to produce a low-cost vacuum package 30. Topcap 28 maybe an anti-reflective coated silicon window. Item 30 is regarded as anintegrated vacuum package (IVP). Between topcap 28 and substrate 29 is acavity 31 that contains detectors 17. There is a seal ring 32 forwafer-to-wafer sealing of cavity 31 between topcap 28 and substrate 29.Gold pads 31 are for wire bonding the connections to detectors 17.Cavity 31 may be evacuated via a port through the back of substrate orwafer 29. This low-cost vacuum encapsulation adds negligible weight(i.e., about 0.02 grams) to detector array 14. A hermetically sealed30×30 mosaic IVP TE sensor may have an overall die size of about 5 mm×5mm.

For this non-imaging application, a 2D array is not required, but foradequate sensitivity it is necessary to use a mosaic of many individualTE detectors 17, electrically interconnected, to form a larger-area“mosaic” TE IR sensor 10, because the NETD improves as the square rootof the mosaic area. Thus, a 30×30 mosaic is 30 times more sensitive thanone unit cell 17, and can provide very good performance even with narrowradiation bandwidth. IVP sensors 14 have long vacuum lifetimes (over 10years), operate up to 180° C., and can be easily handled likeconventional silicon electronic chips. These IR sensors may be producedin volume production (i.e., thousands) at very little cost each.

FIG. 5 shows sensor 10 having multi-band capability utilizing a mosaicof IR bandpass filters. The multi-band capability of IR detectors 17 maybe provided by fabricating narrow-band interference filters 34 directlyon the inner surface of the IVP topcap 28 using a photolithographicprocess to generate alternating IR transmission bandpass filters with 75um periodicity, matching the 75 um periodicity of the underlying TEdetectors 17. A very simple dielectric stack may be employed to producethe selected IR bandpass filters. FIG. 6 reveals a calculatedtransmission of two thin-film interference filters (8 layers of Si andSiO₂) with transmission peaks 35 and 36 at 8 um and 10 um, respectively(20 cm-1 corresponds to about 200 nm wavelength width).

For a dual-band sensor, alternate TE detectors may be electricallyinterconnected in series and/or parallel, so that sensor 10 mayautomatically produce separate electrical signal voltages for each IRwaveband, with approximately equivalent, about the same or essentiallyidentical fields of view. A detector 17 near the edge of array 14 onsubstrate 29 may have a different field of view than a detector 17 inthe center of array 14 because the side or edge of topcap 28 mayobstruct part of the view from the outside to the detector 17 near theedge, whereas such obstruction would not be present for detector 17 inthe center. There may be a number of detectors of the same wavelength inthe array which make up a group of detectors 17. Detectors 17 of thesame group and wavelength may be connected together with series orparallel electrical connections or a combination of such connections.The distribution of the detectors for the various wavelengths may besuch that the group has a cumulative, composite, average or resultantfield of view representative of the group's constituent detectors 17.The result is that the fields of view of the groups may be essentiallythe same or equivalent. FIG. 7 shows an example of five groups ofdetectors 17, one group for each wavelength or “color”. Detectors 17labeled “1” are of group 1, labeled “2” are of group 2, and so on. Thecolors (i.e., various wavelengths) can be distributed according to aregular pattern, which probably may be designed differently fordifferent numbers of colors, but the general principle is the same. Thevarious “colored” detectors 17 comprising the mosaic are distributedacross the mosaic area, so that each individual “color” detector 17 hasa substantially-equal number of near neighbors of each of the other“colors”. All individual detectors of each separate color areelectrically connected together (either in series, parallel or acombination thereof) to give a single output signal of that “color” andincorporating a field of view for the respective group. There may be acase in which the colors are distributed randomly, which achievessubstantially the same equalization of the fields of view among thegroups, even though a regular pattern is not used. Various “colored”detectors 17 comprising the mosaic may be distributed randomly acrossthe mosaic area, so that each individual “color” detector 17 has, on theaverage, a substantially-equal number of near neighbors of each of theother “colors”. All individual detectors 17 of each separate color maybe electrically connected together (either in series or parallel, butusually in series) to give a single output signal of that “color”. Therandom configuration may work better when the number of detectors inarray 14 is large (i.e., greater than 50).

The wavelength or “color” of a detector 17 may be determined by thefilter 34 situated between the sensing surface or junction of detector17 and that which is observed. FIG. 5 reveals a perspective of filters34 relative to detectors 17. Filters 34 designate the “colors” fordetectors 17. The filters 34 are laid out according to groups asdescribed above. FIG. 8 is a side view of the relationship of filter 34to detector 17. Filters 34 may be put on the inside surface of topcap 28with photolithographic processes.

The advantages of TE infrared thermal detectors 17 in the present sensor10 include Low cost (because of the use of commercial siliconfabrication and vacuum package process), robustness (>12,000-g's, 180°C. tolerant, and European Space Agency space-qualified), suitability forlong integration times (un-measurable 1/f sensor noise), highsensitivity (NETD <10 mK with 20 cm-1 IR bandwidth), broadbandresponsivity (<3 to >15 μm), and ease of operation (uncooled, no thermalstabilization or bias voltage required, direct dc signal voltage).Sensor 10 may utilize other kinds of detectors 17.

The NETD of a 2.5 mm square 30×30 mosaic IVP TE sensor 10 may becalculated to be <10 mK in the operating mode of the program with 10seconds integration time, 20 cm-1 waveband near 10 um, 290 K targettemperature, and F/1 optical aperture. The NESR may be computed to be5.4 e–10 W/cm2.sr.cm-1. Two such IR detectors 17 may be placed side byside, viewing the sky via two IR thin-film multilayer filters 34centered at (in the case of GB) 9.8 um and 8.0 um, to give a goodsignal/noise ratio (10:1 for CL=100 mg/m2) for GB under most atmosphericconditions.

Sensor 10 electronics may include a CMOS electronic circuit 40 as shownin FIG. 9 may be used to compute the IR ratio signal of a backgroundsignal and a gas detection signal from corresponding detectors 17 toinputs 37 and 38, respectively. IR detector signals pass throughpreamplifiers 41 and 42 and are digitized with a microprocessor 39operating in a sigma-delta feedback loop. The ratio signal may beaccessed at output 43. An RF link may be connected to output 43. Circuit40 uses 150 uA at 3V (0.5 mW).

Discrimination between chemical agents and interferents may be detected.The military M21 remote sensing chemical agent alarm and joint servicelightweight standoff chemical agent detector (JSLSCAD), which are remotechemical agent sensors, measure the radiance at multiple narrowwavebands within the range 800 to 1200 wavenumbers, where atmospherictransmission is normally good (except for the ozone doublet near 1030cm-1) and chemical agents have distinctive spectral characteristics.Curves 44, 45 and 46 in FIGS. 10 a, 10 b and 10 c show the absorptivitycoefficients of chemical nerve agent GB, and two common battlefieldinterferents, white phosphorus (WP) smoke and Fort Benning dust (dust)near 10 um wavelength, respectively.

In order to differentiate chemical agents from each other, and frominterferents, at least two, and possibly many, different IR wavebandsmust be measured. For example, looking at FIGS. 10 a, 10 b and 10 c, therelative fractional radiance change at 8.0 um (1250 cm⁻¹) compared to9.8 um (1020 cm⁻¹) appears small for GB, but significant for either WPor dust. The spectral resolution that has been used (with M21 andJSLSCAD) to detect and differentiate chemical agents against complexbackground IR signatures may be 4 wavenumbers. This however may require100 IR measurement bands to cover the full 8–12 um spectral range, whichseems not conducive to a low-cost sensor. Fortunately, the skywardviewing geometry of the proposed sensor greatly simplifies thebackground IR signature, so that a fewer number of wider spectral bandsmay be used. Since the minimum practical number, and width, of thewavebands for reliable species identification may need to be determined,one could analytically determine how a variation in the number of IRbands and bandwidths affect the ability of the proposed sensor todiscriminate chemical agents from harmless atmospheric contaminants(dust, smoke, etc.) and discriminate different classes and types ofchemical agents from each other. One may use IR spectra. One may takeinto account recent improvements in signal processing and patternrecognition techniques (autoregressive (AR) modeling, Markov RandomField (MRF) and neutral net processing. One may select the smallestnumber of IR bands, with the widest wavebands, that may produce a usefulpractical result in sensor 10. The results may be used to determine theoptimum number of IR bands and bandwidths required in a productionsensor.

A look at this has been performed, using JSLSCAD data as a baseline.This is tended to indicate that higher-resolution is more important thanthe number of bands employed. Adequate performance may be attained withfive to eight wavebands, with full width half maximum (FWHM) of 16 cm-1(approx 0.2 um). Suitable center-wavebands for various agents areindicated as follows: GA, 1046 cm-1; GB, 1026 cm-1; GD, 1022 cm-1; GF,1016 cm-1; VX, 1038 cm-1; HD, 1231 cm-1; HN3, 1121 cm-1; and Lewisite,814 cm-1.

An 8–12 um sensor 10 may be fabricated using circuit 40 of FIG. 9.Sensor 10 may use one 45 degree field of view (FOV) 30×30 mosaic IVP TEIR sensor on one channel, with the other channel being used to measureair temperature with a thermistor. This may be a dual-band IVP TE sensor10 calibrated radiometer. The 30×30 mosaic TE IVP sensor 10 may beplaced in a circular aluminum optical shroud on a circuit board. Twochips, amplifiers 15 (41, 42) and microprocessor 16 (39), and array 14may be placed on circuit board 47.

For the lowest cost and weight, sensor 10 may use no lens and rely onthe overhead chemical agent filling the vertical field of view (FOV). Ifno lens is used, then incident rays from the sky within the FOV may passthrough the narrow-band IR filters at varying angles of incidence. Inthis case, one may consider the change in IR filter characteristics withangle of incidence. The computed change in center wavelength of a 10 μmbandpass filter as a function of angle of incidence of the radiationshows that plus/minus 25 degrees (i.e., about F/1) may be acceptable, sono collimating lens should be required for 20 cm-1 wavebands and F/1FOV. A germanium window may be used to provide environmental protection.The window may be made optically diffusing, to provide more uniformfields of view to IR detectors 17. Curve 48 of FIG. 11 shows the effectof variation of an angle of incidence on a generic narrow-band filtercentered at 1000 cm-1 (10 um wavelength).

It is significant that the fields of view of the groups of detectors 17for the different IR bands be essentially identical, so that pointobjects (dust specs, isolated clouds, etc.) do not affect one band morethan another. This may be substantially achieved by the use of a mosaicof IR detector 17 and IR filters 34, with every detector operating inone band being surrounded by other sensors operating in the differentbands, as described above. Impinging radiation 27 field can also besubstantially randomized by the use of an “integrating sphere” 50 asshown in FIG. 12. Radiation 27 may enter a portal 51 of sphere 50.Radiation 27 is reflected around internally in sphere 50 by thereflective inside surface of sphere 50. Randomized radiation 53 may exitfrom sphere 50 through portal 52. However, sensor 10 may be placed atthe portal 52 exit of sphere 50 to detect the radiation.

Sensor 10 has high shock tolerance. IR detectors 17 have been tested to14,000 g, and may tolerate more than 20,000 g. Electronic circuits maybe hardened to 20,000 g by encapsulation in supporting media. Lenscomponents might be able to tolerate 20,000 g with suitable robustmounts.

Weight, size and power of sensor 10 may be favorable for many users.Using the known density of materials, one may estimate the weight of theexpected components of chemical agent sensor 10. A single band sensor 10is reviewed in the weight calculation table 54 in FIG. 13. Additionalinfrared bands may be added with little additional impact insize/weight/power/cost.

The present detector system 60 may receive emissions 56 from a gas cloudor sample 55. System 60 may be mounted so as to receive emissions orradiation 56 from the sky or the ground. The spectrum of the cloud orsample may be better detected if the cloud or sample 55 is at atemperature different from the sky or the ground. System 60 may be astand off detector in that it detects gas at a distance. Another kind ofsensor may be a point sensor in that it is in the gas being detected,i.e., it may be pointed into the gas. Emissions or incident radiation56, for instance, may propagate through a collimating lens 57 to beamsplitter 58. Lens 57 may be composed of an infrared transparent materialsuch as Ge. Splitter 58 may have about a 50/50 ratio split betweentransmittance and reflection. A thin layer of infrared reflectivematerial such as aluminum may be deposited on or applied to a flatsurface on the front of the infrared transparent material of splitter 58facing the incident radiation 56. Incident radiation or beam 56 may besplit into beams 61 and 62 by splitter 58. Beam 61 may go from splitter58 to be reflected by fixed mirrors 63 and 64 in that order, and then atleast partially pass through splitter 58 to a cylindrical focusing lens65. Beam 62 may emanate from splitter 58 towards mirror 64 and bereflected towards mirror 63 which in turn may reflect beam 62 tosplitter 58. Splitter 58 may reflect at least a portion of beam 62 tolens 65. Beams 61 and 62 may meet at an area 66 on the top flat surfaceof lens 65 to interfere with each other to form a fringe or interferencepattern 81 having fringes or lines 82.

Lens 65 may magnify or focus in one dimension, in that it may have onedimension of curvature. The lens 65 material may be composed of someinfrared transparent substance such as Ge. Ordinary glass does notappear to adequately transmit such IR light.

The lens 57, splitter 58, and fixed mirrors 63 and 64 may constitute astationary linear fringe interferometer. Use of a stationaryinterferometer may result in better sensitivity and resolution than aninterferometer with a moveable mirror 63 or 64. Minor movement of anunfixed mirror may adversely affect the performance of theinterferometer, even if the moveable mirror is supposedly adjusted foroptimal performance.

Light beams 61 and 62 may impinge about an area 66. If light beams 61and 62 interfere, there may be the fringe pattern 81 having fringes orinterference lines 82, as shown in area 66 on the top flat surface ofcylindrical lens 65 in FIG. 14 and of pattern 81 in FIG. 15. Pattern 81in the graph is an illustrative example of a number, shape and intensityof fringes which may be different for various systems. The graph showsthe intensity of the light impinging the top surface of lens 65 versusdistance in the direction of the length of longitudinal axis of lens 65.The lines or fringes 82 of interference pattern 81 may be focused bylens 65 onto detectors 76 situated in a linear array 67. The lines orfringes may be individually focused on respective detectors 76. Eachdetector 75 may sense the light and its intensity at each increment ofdistance of the pattern 81, and convert its respective intensitylocations into electrical signal representing the intensity of the lightat each of the detectors 76 in array 67, of which the electrical signalstogether may provide an electrical representation of interferencepattern 81. Linear array 67 may be a row of about 120 uncooled infrareddetectors such as microbolometers, in a case of an illustrative example.The number of detectors may be more or less than 120. Themicrobolometers may be reasonable in cost and do not need to be cooled.

The output signals from the array 67 may be low level voltages and easyto manage with the present electronics. The uncooled infrared detectors76 may provide broadband detection from about one to fifty microns. Atypical range of infrared detection may be between about 3 and 12microns. On the other hand, there may be visible and ultra-violet lightdetectors 76 in the array for other band detection. The whole system 60may be designed to detect most fluids (i.e., gases or liquids) or bedesigned for optimized detection of a particular fluid.

Items 82 of the plot in FIG. 15 may represent the interference pattern81 of the impinging light. There may be more or less fringes or lines82, each of which may be focused on a detector 76 in the linear array67. The electrical signals 68, which may be electrical equivalents ofthe lines or fringes 82 impinging the detectors 76, may be conveyed fromarray 67 via a conductive line to an analog-to-digital converter (ADC)69. The signals 68 may be converted into digital signals 71representative of intensities of the light impinging each of thedetectors 76 in array 67. The detectors 76 may be situated in anintegrated vacuum package (IVP) 77 with a window over the detectors tomaintain the integrity of the package. The signals 71 may be sent to amicroprocessor 72 in either a serial or parallel format. These signals71 may be processed or deconvolved into data that provides a pattern ofa “fingerprint” or other identifying pattern of the sample gas or gases55. The conversion of signals 71 to signals 73 constituting anidentifying pattern may be performed by processor 72 utilizing anavailable Fourier transform program. FIG. 16 shows a graphicalrepresentation of such pattern 83 having features 84 in terms ofintensity versus wavelength. Processor 72 may have an analyzer with alook-up table to recognize a pattern 83 or the electronic signals 68from the array 67. Pattern 83 may be displayed on display 74. The output73 of processor 72 may include identification of the detected gas orgases by name or otherwise, and provide an overall relative intensityand average wavelength or frequency of the gas radiation, in addition tothe spectrum such as the intensity versus wavelength or power versusfrequency data, for example. The spectrum may be expressed in varioussets of terms. Other information may be provided by processor 72. Theoutput 73 of processor 72 may go to a display 74, so that the observermay observe the data, graphs, and processor analyses. Each analysis inan illustrative example may cover about 100 different wavelengths. Thenumber of wavelengths may instead be more or less that 100. An output 73to an audio emanating device 75 and display 74 may be provided to theuser in terms of intensities, wavelengths, and identities of the gases,or other kinds of parameters or data. Also, the display 74 and device 75may provide visible and audio warnings about the presence of certaingases and their intensities, particularly if they are considereddangerous in particular areas. There may be warning lights and alarms.The output 73 may also go to a printer 78 and an external connection 79.

The sensor may be constructed with available and inexpensive parts toresult in reasonable, practical, reasonable and saleable product. Thesystem 60 may be put into a package, for example, of about a 10 cm cube,excluding the printer 78. This package may also exclude warning lights,alarms and sirens. It may or might not include the display and audiodevice. System 60 and its package may have the flexibility of beingdesigned to fit the needs or desires of the user.

Although the invention has been described with respect to at least oneillustrative embodiment, many variations and modifications will becomeapparent to those skilled in the art upon reading the presentspecification. It is therefore the intention that the appended claims beinterpreted as broadly as possible in view of the prior art to includeall such variations and modifications.

1. A chemical agent sensor comprising: an interferometer having a lightinput and output; an array of light detectors proximate to the output ofthe interferometer; and a processor connected to the array; and wherein:the array is a linear array; and the interferometer is a linear fringeinterferometer.
 2. The sensor of claim 1, wherein the lens is acylindrical lens having a longitudinal axis approximately parallel tothe longitudinal dimension of the linear array.
 3. The sensor of claim2, wherein the light detectors are infrared light detectors.
 4. Thesensor of claim 3, wherein the linear array of light detectors arearranged so that some detectors are positioned to detect a differentrange wavelengths than another detector in the array.
 5. The sensor ofclaim 4, wherein the detectors are uncooled intensity detectors oflight.
 6. The sensor of claim 5, wherein the processor has an intensityversus wavelength display.
 7. The sensor of claim 6, wherein light froma gas enters the light input of the interferometer.
 8. The sensor ofclaim 7, wherein the processor comprises a Fourier transform mechanism.9. The sensor of claim 8, wherein the processor comprises a gasidentification indicator.
 10. The sensor of claim 9, wherein theindicator is a display.
 11. The sensor of claim 9, wherein the indicatoris an audio device.
 12. The sensor of claim 9, wherein the indicator isa printer.
 13. A means for sensing gas, comprising: means for receivinglight emanated by the gas; means for interfering the light into a linearfringe pattern; means for detecting the linear fringe pattern of lightand converting the pattern into electrical signals; and means forprocessing the electrical signals into an intensity versus wavelengthparameters of the gas; and wherein the means for detecting is uncooledinfrared detection.
 14. A method for sensing gas, comprising: receivinglight emanated by the gas; interfering the light into a pattern ofintensity versus distance; detecting the pattern and converting thepattern into electrical signals; and processing the electrical signalsinto a pattern of intensity versus distance; and wherein the detectingis performed with uncooled infrared detectors.
 15. The method of claim14, wherein the processing comprises a Fourier transform mechanism. 16.An apparatus for sensing a fluid, comprising: an interferometer havingan input proximate to the fluid and having an output; a linear array ofinfrared light detectors proximate to the output; a processor connectedto detectors; and an intensity versus wavelength output device connectedto the processor; and wherein light from the fluid into the input of theinterferometer is output from the interferometer in a distance versuswavelength fringe pattern.
 17. The apparatus of claim 16, wherein theoutput device provides intensity versus wavelength data about the fluid;and the output device identifies the fluid proximate to the input. 18.The apparatus of claim 16, wherein light from the fluid into the inputof the interferometer is output from the interferometer in a distanceversus wavelength linear fringe pattern.
 19. The apparatus of claim 18,wherein the interferometer comprises a first lens at the input; aninfrared light splitter proximate to the lens and the output; a firstmirror proximate to the splitter; and a second mirror proximate to thesplitter and the first mirror.
 20. The apparatus of claim 19, whereinthe first and second mirrors are fixed relative to each other.
 21. Theapparatus of claim 20, wherein the fringe pattern is converted by thearray of detectors into electrical signals.
 22. The apparatus of claim21, wherein the processor converts the electrical signals to spectrumdata of the fluid.
 23. The apparatus of claim 22, wherein the processoridentifies the fluid.
 24. The apparatus of claim 23, wherein theprocessor utilizes a Fourier transformation to convert the electricalsignals to spectrum data of the fluid.
 25. The apparatus of claim 24,wherein the detectors are uncooled.
 26. The apparatus of claim 25,further comprising second lens that is a longitudinal focusing lenssituated between the output of the interferometer and the array.
 27. Theapparatus of claim 26, wherein: the first lens is a collimating lens;the first lens is transparent to infrared light; the second lens istransparent to infrared light; and the splitter is reflective ofinfrared light and transparent to infrared light.
 28. The apparatus ofclaim 27, wherein the spectrum data are intensity versus wavelength. 29.The apparatus of claim 27, wherein the spectrum data are power versusfrequency.